Employees at Pfizer Inc's U.S. research centers, such as the La Jolla, California site that specializes in cancer drugs, may want to dust off their resumes if the company's proposed acquisition of Britain's AstraZeneca comes to fruition. Pfizer said on Friday it was determined to reach a deal that would restore its status as the world's biggest pharmaceutical company despite AstraZeneca's rejection of its latest cash and stock offer of 63 billion pounds ($106 billion). To reassure the British government about its proposal, Pfizer has promised the combined company would keep 20 percent of its research and development workforce in the country.